1. Field of the Invention
The invention relates to an information communication system, and, more particularly, the invention relates to an information communication system with collision avoidance.
2. Description of the Prior Art
The prior art shows information communication systems which are added to computers to allow various remotely located users to access the computer. At first, access to the central computer was accomplished by tying the remote device, for example, a console to one access port of the computer. As the demand for communication between various users including several large scale data processing computers increased the overhead of providing access of many users to the computer increased. That overhead included both hardware and software. One desired feature of a multi-user communication system is that the information be broadcast over a common broadcast channel having a fixed total capacity. Various information communication systems were devised to provide the desired result.
One such solution is shown in U.S. Pat. No. 4,063,220 issued to Metcalfe et al on Dec. 13, 1977 and entitled "Multipoint Data Communication System With Collision Detection", and U.S. Pat. No. 4,099,024 issued to Boggs et al on July 4, 1978 and entitled "Communications Network Repeater". The Metcalfe and Boggs patents show and describe a communications system which utilizes a series of repeaters which are capable of detecting when they are both receiving and transmitting information. The repeater after it detects a collision on one communication medium causes a transmission by its corresponding transceiver connected to the other communication medium. This causes the collision device which is attached to each of the transceivers to be actuated which in turn causes the transmitting device to terminate its transmission. The transmitting device then utilizes a random number generator within the transceiver and various other methods to cause an arbitration to occur between the two devices transmitting. It is possible, however, that both devices will begin transmitting again at the same time and a collision can recur. This possibility is present because the communication medium which generally would comprise a coaxial cable has a propagation delay. Further, the transmitted signal is attenuated along the cable. The repeaters shown in the Boggs and Metcalfe patents reduce the attenuation problem. However, collisions can still occur which require the system to arbitrate the collisions prior to retransmission of the information.
Various other solutions to the common broadcast channel collision avoidance problem are described in an article by Kleinrock in the 1977 IFIP Congress Proceedings at page 547 and entitled "Performance of Distributed Multi-Access Computer-Communication Systems". For example, one solution is to provide each user with a time slot wherein the user can transmit any information which it desires. Several systems are described where the information (or as referred to in the article, messages) transmitted or allowed to collide and the information must then be retransmitted.
None of the prior constructions shows and describes a communications system which utilizes charging of the coaxial cable with a unique predetermined DC voltage for each using device to determine if any of the other using devices are preparing to transmit in order to avoid any collisions of information signals being transmitted.